This invention relates to the preparation of cast elastomers by reaction of organic polyisocyanates with aminocrotonate-terminated polyethers containing isocyanate-reactive amino groups having moderated reactivity.
Aminocrotonate-terminated polyethers are known. E.g., U.S. Pat. Nos. 3,666,726, 5,066,824, 5,151,470, and 5,231,217. The casting of polyurethane elastomers in open molds is also known. E.g., A. Awater, "PU cast elastomers" in Polyurethane Handbook, ed. G. Oertel (New York: Hanser Publishers, 1985), pages 372-388; J. H. Saunders and K. C. Frisch, "Urethane Elastomers" in Polyurethanes. Chemistry and Technology (New York: Interscience Publishers, 1962), pages 273-314. However, aminocrotonate-terminated polyethers have most typically been used for reaction injection molding, in which relatively rapid reaction of isocyanate components with isocyanate-reactive components is desired. E.g., U.S. Pat. No. 5,356,946 and U.S. application Ser. No. 07/699,529 (filed May 14, 1991). Such reactivities are not generally considered suitable for preparing cast elastomers in open molds.
It has now been found, however, that cast elastomers having good mechanical properties can be prepared using aminocrotonate-terminated polyethers containing amino groups having reduced reactivity toward organic polyisocyanates.